util-linux/coreutils/tail.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * Mini tail implementation for busybox
   4  *
   5  * Copyright (C) 2001 by Matt Kraai <kraai@alumni.carnegiemellon.edu>
   6  *
   7  * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
   8  */
   9
  10 /* BB_AUDIT SUSv3 compliant (need fancy for -c) */
  11 /* BB_AUDIT GNU compatible -c, -q, and -v options in 'fancy' configuration. */
  12 /* http://www.opengroup.org/onlinepubs/007904975/utilities/tail.html */
  13
  14 /* Mar 16, 2003      Manuel Novoa III   (mjn3@codepoet.org)
  15  *
  16  * Pretty much rewritten to fix numerous bugs and reduce realloc() calls.
  17  * Bugs fixed (although I may have forgotten one or two... it was pretty bad)
  18  * 1) mixing printf/write without fflush()ing stdout
  19  * 2) no check that any open files are present
  20  * 3) optstring had -q taking an arg
  21  * 4) no error checking on write in some cases, and a warning even then
  22  * 5) q and s interaction bug
  23  * 6) no check for lseek error
  24  * 7) lseek attempted when count==0 even if arg was +0 (from top)
  25  */
  26
  27 #include "libbb.h"
  28
  29 static const struct suffix_mult tail_suffixes[] = {
  30         { "b", 512 },
  31         { "k", 1024 },
  32         { "m", 1024*1024 },
  33         { "", 0 }
  34 };
  35
  36 struct globals {
  37         bool status;
  38 } FIX_ALIASING;
  39 #define G (*(struct globals*)&bb_common_bufsiz1)
  40
  41 static void tail_xprint_header(const char *fmt, const char *filename)
  42 {
  43         if (fdprintf(STDOUT_FILENO, fmt, filename) < 0)
  44                 bb_perror_nomsg_and_die();
  45 }
  46
  47 static ssize_t tail_read(int fd, char *buf, size_t count)
  48 {
  49         ssize_t r;
  50         off_t current;
  51         struct stat sbuf;
  52
  53         /* /proc files report zero st_size, don't lseek them. */
  54         if (fstat(fd, &sbuf) == 0 && sbuf.st_size > 0) {
  55                 current = lseek(fd, 0, SEEK_CUR);
  56                 if (sbuf.st_size < current)
  57                         xlseek(fd, 0, SEEK_SET);
  58         }
  59
  60         r = full_read(fd, buf, count);
  61         if (r < 0) {
  62                 bb_perror_msg(bb_msg_read_error);
  63                 G.status = EXIT_FAILURE;
  64         }
  65
  66         return r;
  67 }
  68
  69 #define header_fmt_str "\n==> %s <==\n"
  70
  71 static unsigned eat_num(const char *p)
  72 {
  73         if (*p == '-')
  74                 p++;
  75         else if (*p == '+') {
  76                 p++;
  77                 G.status = 1; /* mark that we saw "+" */
  78         }
  79         return xatou_sfx(p, tail_suffixes);
  80 }
  81
  82 int tail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  83 int tail_main(int argc, char **argv)
  84 {
  85         unsigned count = 10;
  86         unsigned sleep_period = 1;
  87         bool from_top;
  88         const char *str_c, *str_n;
  89
  90         char *tailbuf;
  91         size_t tailbufsize;
  92         unsigned header_threshhold = 1;
  93         unsigned nfiles;
  94         int i, opt;
  95
  96         int *fds;
  97         const char *fmt;
  98
  99 #if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
 100         /* Allow legacy syntax of an initial numeric option without -n. */
 101         if (argv[1] && (argv[1][0] == '+' || argv[1][0] == '-')
 102          && isdigit(argv[1][1])
 103         ) {
 104                 count = eat_num(argv[1]);
 105                 argv++;
 106                 argc--;
 107         }
 108 #endif
 109
 110         /* -s NUM, -F imlies -f */
 111         IF_FEATURE_FANCY_TAIL(opt_complementary = "s+:Ff";)
 112         opt = getopt32(argv, "fc:n:" IF_FEATURE_FANCY_TAIL("qs:vF"),
 113                         &str_c, &str_n IF_FEATURE_FANCY_TAIL(,&sleep_period));
 114 #define FOLLOW (opt & 0x1)
 115 #define COUNT_BYTES (opt & 0x2)
 116         //if (opt & 0x1) // -f
 117         if (opt & 0x2) count = eat_num(str_c); // -c
 118         if (opt & 0x4) count = eat_num(str_n); // -n
 119 #if ENABLE_FEATURE_FANCY_TAIL
 120         /* q: make it impossible for nfiles to be > header_threshhold */
 121         if (opt & 0x8) header_threshhold = UINT_MAX; // -q
 122         //if (opt & 0x10) // -s
 123         if (opt & 0x20) header_threshhold = 0; // -v
 124 # define FOLLOW_RETRY (opt & 0x40)
 125 #else
 126 # define FOLLOW_RETRY 0
 127 #endif
 128         argc -= optind;
 129         argv += optind;
 130         from_top = G.status; /* 1 if there was "-c +N" or "-n +N" */
 131         G.status = EXIT_SUCCESS;
 132
 133         /* open all the files */
 134         fds = xmalloc(sizeof(fds[0]) * (argc + 1));
 135         if (!argv[0]) {
 136                 struct stat statbuf;
 137
 138                 if (fstat(STDIN_FILENO, &statbuf) == 0
 139                  && S_ISFIFO(statbuf.st_mode)
 140                 ) {
 141                         opt &= ~1; /* clear FOLLOW */
 142                 }
 143                 argv[0] = (char *) bb_msg_standard_input;
 144         }
 145         nfiles = i = 0;
 146         do {
 147                 int fd = open_or_warn_stdin(argv[i]);
 148                 if (fd < 0 && !FOLLOW_RETRY) {
 149                         G.status = EXIT_FAILURE;
 150                         continue;
 151                 }
 152                 fds[nfiles] = fd;
 153                 argv[nfiles++] = argv[i];
 154         } while (++i < argc);
 155
 156         if (!nfiles)
 157                 bb_error_msg_and_die("no files");
 158
 159         /* prepare the buffer */
 160         tailbufsize = BUFSIZ;
 161         if (!from_top && COUNT_BYTES) {
 162                 if (tailbufsize < count + BUFSIZ) {
 163                         tailbufsize = count + BUFSIZ;
 164                 }
 165         }
 166         tailbuf = xmalloc(tailbufsize);
 167
 168         /* tail the files */
 169         fmt = header_fmt_str + 1; /* skip header leading newline on first output */
 170         i = 0;
 171         do {
 172                 char *buf;
 173                 int taillen;
 174                 int newlines_seen;
 175                 unsigned seen;
 176                 int nread;
 177                 int fd = fds[i];
 178
 179                 if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
 180                         continue; /* may happen with -E */
 181
 182                 if (nfiles > header_threshhold) {
 183                         tail_xprint_header(fmt, argv[i]);
 184                         fmt = header_fmt_str;
 185                 }
 186
 187                 if (!from_top) {
 188                         off_t current = lseek(fd, 0, SEEK_END);
 189                         if (current > 0) {
 190                                 unsigned off;
 191                                 if (COUNT_BYTES) {
 192                                 /* Optimizing count-bytes case if the file is seekable.
 193                                  * Beware of backing up too far.
 194                                  * Also we exclude files with size 0 (because of /proc/xxx) */
 195                                         if (count == 0)
 196                                                 continue; /* showing zero bytes is easy :) */
 197                                         current -= count;
 198                                         if (current < 0)
 199                                                 current = 0;
 200                                         xlseek(fd, current, SEEK_SET);
 201                                         bb_copyfd_size(fd, STDOUT_FILENO, count);
 202                                         continue;
 203                                 }
 204 #if 1 /* This is technically incorrect for *LONG* strings, but very useful */
 205                                 /* Optimizing count-lines case if the file is seekable.
 206                                  * We assume the lines are <64k.
 207                                  * (Users complain that tail takes too long
 208                                  * on multi-gigabyte files) */
 209                                 off = (count | 0xf); /* for small counts, be more paranoid */
 210                                 if (off > (INT_MAX / (64*1024)))
 211                                         off = (INT_MAX / (64*1024));
 212                                 current -= off * (64*1024);
 213                                 if (current < 0)
 214                                         current = 0;
 215                                 xlseek(fd, current, SEEK_SET);
 216 #endif
 217                         }
 218                 }
 219
 220                 buf = tailbuf;
 221                 taillen = 0;
 222                 /* "We saw 1st line/byte".
 223                  * Used only by +N code ("start from Nth", 1-based): */
 224                 seen = 1;
 225                 newlines_seen = 0;
 226                 while ((nread = tail_read(fd, buf, tailbufsize-taillen)) > 0) {
 227                         if (from_top) {
 228                                 int nwrite = nread;
 229                                 if (seen < count) {
 230                                         /* We need to skip a few more bytes/lines */
 231                                         if (COUNT_BYTES) {
 232                                                 nwrite -= (count - seen);
 233                                                 seen = count;
 234                                         } else {
 235                                                 char *s = buf;
 236                                                 do {
 237                                                         --nwrite;
 238                                                         if (*s++ == '\n' && ++seen == count) {
 239                                                                 break;
 240                                                         }
 241                                                 } while (nwrite);
 242                                         }
 243                                 }
 244                                 if (nwrite > 0)
 245                                         xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
 246                         } else if (count) {
 247                                 if (COUNT_BYTES) {
 248                                         taillen += nread;
 249                                         if (taillen > (int)count) {
 250                                                 memmove(tailbuf, tailbuf + taillen - count, count);
 251                                                 taillen = count;
 252                                         }
 253                                 } else {
 254                                         int k = nread;
 255                                         int newlines_in_buf = 0;
 256
 257                                         do { /* count '\n' in last read */
 258                                                 k--;
 259                                                 if (buf[k] == '\n') {
 260                                                         newlines_in_buf++;
 261                                                 }
 262                                         } while (k);
 263
 264                                         if (newlines_seen + newlines_in_buf < (int)count) {
 265                                                 newlines_seen += newlines_in_buf;
 266                                                 taillen += nread;
 267                                         } else {
 268                                                 int extra = (buf[nread-1] != '\n');
 269                                                 char *s;
 270
 271                                                 k = newlines_seen + newlines_in_buf + extra - count;
 272                                                 s = tailbuf;
 273                                                 while (k) {
 274                                                         if (*s == '\n') {
 275                                                                 k--;
 276                                                         }
 277                                                         s++;
 278                                                 }
 279                                                 taillen += nread - (s - tailbuf);
 280                                                 memmove(tailbuf, s, taillen);
 281                                                 newlines_seen = count - extra;
 282                                         }
 283                                         if (tailbufsize < (size_t)taillen + BUFSIZ) {
 284                                                 tailbufsize = taillen + BUFSIZ;
 285                                                 tailbuf = xrealloc(tailbuf, tailbufsize);
 286                                         }
 287                                 }
 288                                 buf = tailbuf + taillen;
 289                         }
 290                 } /* while (tail_read() > 0) */
 291                 if (!from_top) {
 292                         xwrite(STDOUT_FILENO, tailbuf, taillen);
 293                 }
 294         } while (++i < nfiles);
 295
 296         tailbuf = xrealloc(tailbuf, BUFSIZ);
 297
 298         fmt = NULL;
 299
 300         if (FOLLOW) while (1) {
 301                 sleep(sleep_period);
 302
 303                 i = 0;
 304                 do {
 305                         int nread;
 306                         const char *filename = argv[i];
 307                         int fd = fds[i];
 308
 309                         if (FOLLOW_RETRY) {
 310                                 struct stat sbuf, fsbuf;
 311
 312                                 if (fd < 0
 313                                  || fstat(fd, &fsbuf) < 0
 314                                  || stat(filename, &sbuf) < 0
 315                                  || fsbuf.st_dev != sbuf.st_dev
 316                                  || fsbuf.st_ino != sbuf.st_ino
 317                                 ) {
 318                                         int new_fd;
 319
 320                                         if (fd >= 0)
 321                                                 close(fd);
 322                                         new_fd = open(filename, O_RDONLY);
 323                                         if (new_fd >= 0) {
 324                                                 bb_error_msg("%s has %s; following end of new file",
 325                                                         filename, (fd < 0) ? "appeared" : "been replaced"
 326                                                 );
 327                                         } else if (fd >= 0) {
 328                                                 bb_perror_msg("%s has become inaccessible", filename);
 329                                         }
 330                                         fds[i] = fd = new_fd;
 331                                 }
 332                         }
 333                         if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
 334                                 continue;
 335                         if (nfiles > header_threshhold) {
 336                                 fmt = header_fmt_str;
 337                         }
 338                         while ((nread = tail_read(fd, tailbuf, BUFSIZ)) > 0) {
 339                                 if (fmt) {
 340                                         tail_xprint_header(fmt, filename);
 341                                         fmt = NULL;
 342                                 }
 343                                 xwrite(STDOUT_FILENO, tailbuf, nread);
 344                         }
 345                 } while (++i < nfiles);
 346         }
 347         if (ENABLE_FEATURE_CLEAN_UP) {
 348                 free(fds);
 349         }
 350         return G.status;
 351 }